Development of high-temperature ferromagnetism in SnO2 and paramagnetism in SnO by Fe doping -: art. no. 054402

We report the development of room-temperature ferromagnetism in chemically synthesized powder samples of Sn1-xFexO2 (0.005 <= x <= 0.05) and paramagnetic behavior in an identically synthesized set of Sn1-xFexO. The ferromagnetic Sn0.99Fe0.01O2 showed a Curie temperature T-C=850 K, which is among the highest reported for transition-metal-doped semiconductor oxides. With increasing Fe doping, the lattice parameters of SnO2 decreased and the saturation magnetization increased, suggesting a strong structure-magnetic property relationship. When the Sn0.95Fe0.05O2 was prepared at different temperatures between 200 and 900 degrees C, systematic changes in the magnetic properties were observed. Combined Mossbauer spectroscopy and magnetometry measurements showed a ferromagnetic behavior in Sn0.95Fe0.05O2 samples prepared at and above 350 degrees C, but the ferromagnetic component decreased gradually as preparation temperature approached 600 degrees C. All Sn0.95Fe0.05O2 samples prepared above 600 degrees C were paramagnetic. X-ray photoelectron spectroscopy, magnetometry, and particle induced x-ray emission studies showed that the Fe dopants diffuse towards the surface of the particles in samples prepared at higher temperatures, gradually destroying the ferromagnetism. Mossbauer studies showed that the magnetically ordered Fe3+ spins observed in the Sn0.95Fe0.05O2 sample prepared at 350 degrees C is only similar to 24% of the uniformly incorporated Fe3+. No evidence of any iron oxide impurity phases were detected in Sn1-xFexO2 or Sn1-xFexO, suggesting that the emerging magnetic interactions in these systems are most likely related to the properties of the host systems SnO2 and SnO, and their oxygen stoichiometry.